I like the HF ranking system, where it assigns a number value to the prospect's likely ceiling, then assigns a probability of reaching that ceiling, so it factors in both potential and proximity.
Here's my thoughts on the top four:
Haula already showed he can play as a solid third liner, and I think he can still get a bit better. I have him at a 7B, which is a net of 6.3. I could almost talk myself into 6.5B as well, which would put him at 5.85 and below Kuemper, but I'll stick with 7B.
Kuemper could be a solid starter in the NHL, with a backup potential at the least. I have him at 7.5C, which is a net of 6.0.
Dumba I think has the highest ceiling but also a higher risk of busting. I have him as 8D, which is 5.6.
Tuch is pretty far away and any 18-year-old has high bust opportunity. Top six potential and a first round pick, which is usually safer, puts him at 7C, which is 5.6. Nod to Dumba to break the tie due to higher potential.